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OMNI‐DIRECTIONAL DOWNHOLE EM PROBES*
- Source: Geophysical Prospecting, Volume 34, Issue 4, Jul 1986, p. 569 - 579
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- 27 Apr 2006
Abstract
ABSTRACT
Borehole surveys are usually commissioned to provide structural details as a guide to further drilling. Conductors remote from the hole are readily detected using EM probes. Vectors can be established by noting variations in wavelength, particularly for reversals of polarity. However, several holes in the same area are required to remove rotational ambiguities, and single axis systems may generate spurious anomalies related to errors in alignment. Consequently, a three‐component sensor has been designed to compare the orthogonal response at each depth. Data are expressed in terms of the invariant parameters of the polarization ellipse, and secondary fields are readily identified.